Pseudo-Foster Kennedy syndrome due to idiopathic intracranial hypertension.

Foster-Kennedy syndrome has been diagnosed as a direct compression of the optic nerve due to an expansive process that leads to atrophy. In the contralateral eye there is papillary oedema due to intracranial hypertension secondary to the tumour mass effect. The case is presented of a 12-year-old boy with overweight (BMI 26) with right eye papillary oedema and left optic nerve atrophy, that was casually found in an ophthalmological examination. He had no other symptomatology or personal medical history. The neurological examination was normal, and the urgent cranial computed tomography showed no masses. Lumbar puncture was performed with increased cerebrospinal fluid outflow resistance (28 cm HO). The rest of studies were normal. Until the appearance of neuroimaging, it was believed that Foster-Kennedy syndrome was pathognomonic of intracranial mass in the frontal area. Pseudo-Foster Kennedy syndrome due to idiopathic intracranial hypertension is very rare, and in the few cases that have been reported in the literature, up to 25% of them are asymptomatic.